A PCS aims to convert electric energy from one form to another, for example converting between AC and DC.
A classical PCS is implemented with a three-phase voltage source converter (VSC) and a bidirectional buck-boost DC-DC converter to regulate the voltage and current in the batteries [1], [2]. The galvanic isolation between the grid and the battery pack is provided by a low-frequency transformer. This solution has as advantages a low complexity, due to reduced number of components, well-known control and design techniques, and wide availability of integrated components. The use of a low-frequency transformer is however not suitable to obtain a high-power density conversion system.
An alternative is to employ a high-frequency transformer (HFT) in the DC-DC conversion stage in order to significantly reduce the size and volume of the transformer. Possible topologies for the high-frequency isolated DC-DC converter are dual half-bridge (DHB), dual active-bridge (DAB) [3] or resonant DC-DC converters. A well-known topology consists in a three-phase VSC to interface the grid and a DAB to regulate the voltage and current in the batteries [4], [5]. Nevertheless, the need of a DC-link to decouple the operation of the three-phase VSC from the DC-DC converter is also a limitation in terms of volume and shorter life of the capacitors.
Several single-stage power converters were proposed to perform bidirectional AC-DC power conversion as a possible alternative for the traditional two-stage solutions described above. The use of a matrix converter (MC) for the front-end is an interesting solution as it provides the capability to perform a direct AC to AC conversion without a DC-link. In [6], [7] and [8] the authors propose the use of a three-phase-to-single-phase MC and a full-bridge (FB) to do the interface of a DC source with the grid. These approaches focus on the operation as an inverter to supply the grid, using the converter as a voltage source in the grid side. Issues related with the DC source, that can be for example a storage unit, are not addressed, such as current regulation, charging and discharging methods, protections, current and voltage ripple.
Another publications propose the use of space vector modulation for the same conversion circuit [9], [10] and [11]. However, these authors do not focus on the interface with the DC source, which is, for example, a requirement for energy storage applications. Moreover, the capability to control the power factor is not described.
Using the three-phase-to-single-phase matrix converter as a current source in the grid side is also a possibility. In document US 2011/0007534 A1 and references [12], [13] and [14] modulations to control the power converter as a bidirectional unit are proposed. These solutions allow the current regulation in the storage device but do not allow the control of the power factor, keeping it near unitary.